Internet connectivity is vital to roaming users of recent years. The roaming users desire constant connection, even during roaming. As a result of popularization of wireless Local Area Network (LAN) hot spots and other next generation wireless technologies, such as Worldwide interoperability for Microwave Access (WiMAX), cities are covered with different, overlapping wireless network areas. Therefore, when a user passes through these different overlapping networks, a user node is repeatedly connected and disconnected. Frequent changes in connection and disconnection degrade user experience (user-friendliness). For example, in an instant messaging application, a communication partner in a user's contact list receives frequent notifications of changes in the user's status. A simple file transfer performed between the user and the communication partner is frequently interrupted because of loss of connection. If a download resuming function is not supported, a file is required to be downloaded from the beginning.
When the problem is divided, first, a length of disconnection should be predicted. As a known technique, “link going up” and “link going down” triggers are known. The former indicates that a link will become usable. The latter indicates an amount of time until the link will become unusable. To predict when connection or disconnection will occur, the “link going up” and “link going down” triggers require physical judgment criteria unique to the wireless signal to be actually obtained (refer to Patent Document 1, below). There is a solution method in which data traffic can be routed through use of a method that takes into consideration changes over time, using such prediction (refer to Patent Document 2, below). However, the method using “link going up” and “link going down” is problematic in that, to carry out the function, a mobile node (MN) is required to be physically close to a point of attachment (PoA).
Another approach is to add a lifetime (duration period) to the status. As an example of this approach, binding update (BU) in mobile IP and zero reservation quality of service (QoS) signaling are known. The BU adds a lifetime indicating that the binding is valid. In effect, the binding is maintained during the period of this lifetime even when the node is temporarily disconnected from the network. The zero reservation QoS signaling does not actually reserve resources when the mobile node is temporarily unusable. However, a signaling path that has been set up is saved until the time limit. However, a method such as this faces a problem in that it is unclear how long the mobile node or communication partner node will be disconnected, and approximately when the mobile node or communication partner node will become usable again.
Patent Document 1: Greaves, Jon, Darren; Hughes, Paul; Ma, Chun, Chau; Seminaro, Michael, “System and method for reliable delivery of event information”, US Patent Application Publication No. 20030225883 A1, Dec. 4, 2003
Patent Document 2: Troxel, Gregory Donald; Wiggins, David Paul, “Systems and methods for predictive routing”, U.S. Pat. No. 6,850,524 B1, Feb. 1, 2005
In this way, currently, there is a problem in that a method does not exist to allow the mobile node to know the length of connection loss (non-connected period). There is a document claiming a method in which judgment is made from a wireless strength of a signal detected by the PoA. However, the method is limited in that the method can be used only when the mobile node is within the range of the PoA. The user cannot know when disconnection occurs whether the loss will be short and temporary or will be for a long amount of time. If the amount of time can be predicted, an algorithm for managing power can be efficiently used. A route more advantageous for the user may be able to be decided. In the specification of IEEE 802.21 that is a standardization of this field, notification of when a connection is lost is permitted. However, no hints are provided as to when the connection will be reestablished.